1. Field of the Invention
The present invention relates to an optical recording medium, and more particularly, to an optical recording medium which enables optical recording of high density.
1. Background of the Related Art
Recently, as requests for information recording/reproducing of high density increase, an optical recording medium is gradually on a spreading trend, which records/reproduces information at high density by using the thermal energy of a laser beam or applying the laser beam and magnetic field together.
As an example of an optical recording medium using the thermal energy of a laser beam, there is a phase variation type optical disk which uses the phase variation of a material in a recording layer. As an example of an optical recording medium using a laser beam and magnetic field together, there is an optical magnetic disk.
In case of the phase variation type optical disk, overwriting is directly possible. Also, this optical disk records/reproduces information by optical means only. Therefore, information can be exchanged between respective media.
In case of the optical magnetic disk, repeat recording of information and erasing of information are possible and high density can be facilitated. In this respect, it is expected that the optical magnetic disk is to be developed to the large extent in the future.
The optical magnetic disk records information by forming a magnetic domain on a vertical magnetization thin film using a laser beam and magnetic field, and reproduces information using magneto-optic effect.
An alloy material of rare earth-transition metal(RE-TM) is mainly used as a recording layer of the optical magnetic disk. A ferromagnetic element such as Fe and Co is used as a transition metal, and Tb, Dy, Gd, Sm, and Ho are used as a rare-earth element.
Particularly, such an optical magnetic disk is characterized in that more information is recorded in a unit area and such information is reproduced without any error.
To efficiently record more information in a unit area, there has been suggested a laser-pumped magnetic field modulation method. In this method, a small and stable magnetic domain can be formed by applying a laser pulse and external magnetic field at the same time. However, since the magnetic domain is too smaller than the size of a recording laser beam, there is a problem in reproducing the magnetic domain.
Since the magnetic domain for reproduction is smaller than a diameter of a reproducing laser beam, a signal is applied thereto from an adjacent magnetic domain when reproducing the magnetic domain, thereby increasing noise. If noise increases, signal-to-noise ratio is relatively reduced, thereby generating reproducing error.
To solve such problems, special reproducing methods have been required.
There has been provided a method in which a mechanism is used, which replicates a signal of a recording layer by opening a window of a reproducing layer in a diameter portion of a reproducing laser beam having a high temperature. In this method, magnetization direction of the reproducing layer is horizontal at a room temperature.
There has been also provided a method for making a reproducing signal large by expanding a magnetic domain recorded on the recording layer in the reproducing layer. This is applied in case of high recording density.
In addition to the above methods, there have been provided a multi-valued recording method and a multi-wavelength recording method. In the multi-valued recording method, the recording layer is multilayered for high density recording. In the multi-wavelength recording method, various recording wavelengths are formed.
However, the above related art methods have several problems.
In case of the laser-pumped magnetic field modulation method, although the recording density in the advance direction of a laser beam can be improved, it is difficult to improve the recording density in the disk track direction.
In case of the multi-valued recording method and the multi-wavelength recording method, there are problems that a structure of the disk is complicate and fabrication processes are difficult.
Accordingly, the present invention is directed to an optical recording medium that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an optical recording medium which improves recording density at a simple structure by forming an optical reaction layer of a new material.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, an optical recording medium having a recording layer for recording information through a laser beam, includes an optical reaction layer formed on or below the recording layer, which is melted at a predetermined temperature or causes optical change to vary a refractive index, thereby transmitting the laser beam.
In one embodiment of the present invention, the optical reaction layer is formed of either any one of Ge, As, Se, Sn, Sb, Te and Bi, or their alloy, and is melted at a temperature of 300xcx9c800xc2x0 C. so as to form a transparent window for transmitting the laser beam. Also, a reproducing layer may be formed between the optical reaction layer and the recording layer to reproduce information of the recording layer.
In another aspect, an optical recording medium according to the present invention includes: a substrate; a first dielectric layer formed on the substrate; an optical reaction layer formed on the first dielectric layer, for being melted at a predetermined temperature or causing optical reaction to vary a refractive index, thereby transmitting a laser beam; a second dielectric layer formed on the optical reaction layer; a recording layer formed on the second dielectric layer, for recording information by the laser beam; and a passivation layer formed on the recording layer.
In another embodiment of the present invention, a reproducing layer may be formed between the optical reaction layer and the second dielectric layer to make a reproducing signal large by expanding information transcribed from the recording layer.
In other aspect, an optical recording medium according to the present invention includes: a substrate; a reflecting layer formed on the substrate; a recording layer formed on the reflecting layer, for recording information by a laser beam; a first passivation layer formed on the recording layer; an optical reaction layer formed on the first passivation layer, for being melted at a predetermined temperature or causing optical reaction to vary a refractive index, thereby transmitting the laser beam; and a second passivation layer formed on the optical reaction layer.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.